The present invention relates, in general, to an apparatus and method for detecting landmines and, in particular, to an apparatus with an infrared detector to obtain thermal signatures of the soil surface where a buried landmine might exist and where the apparatus irradiates that soil surface with electromagnetic energy and thermal signatures of that surface are obtained by the detector.
It has been estimated that there are about 110 million anti-personnel (AP) and anti-tank (AT) mines scattered on the ground surface or buried in the ground in about 64 countries. These mines pose a serious threat to any military operation including UN peace-keeping operation and also to unsuspecting civilian populations. In addition, the effect on the local economy is often devastating, as is the case in Afghanistan, Bosnia etc. A mined area can never be safe until it is thoroughly cleared of mines.
The recent international treaty to ban the use of antipersonnel mines by most countries of the world has provided a significant push to eliminate these weapons from the arsenal of mankind and a welcome support to the cause of demining. Unfortunately, modern mines contain very little metal and are difficult to detect using conventional electromagnetic techniques. As a result, there are currently about 20 methods for mine detection at various stages of development. They range from quite simple methods such as the use of dogs to the most sophisticated modern techniques including the use of nuclear quadrupole resonance, thermal neutron activation, acoustic techniques, magnetic measurements using superconducting quantum interference devices (SQUIDs), and chemical detection methods.
For military as well as civilian/humanitarian applications, a successful mine detection method should be inexpensive, easy to use, and should have a fast and accurate detection rate. Further, any new detection method should have superior detection sensitivity, detection rate and a lower false alarm rate than that already available through existing methods. The method should also be forward-looking to avoid the risk of straddling the mine during detection.
Amongst the various detection methods under development, passive infrared (IR) imaging, conventional electromagnetic methods, ground probing radar (GPR), and thermal neutron activation (TNA) are perhaps the most promising techniques. Hyper-spectral imaging is also expected to yield a powerful method for mine detection. While these methods also have their respective limitations, a fusion of data from these sensors could provide a system that may be acceptable for most applications. This fusion of data concept is described in U.S. patent application Ser. No. 09/054,397 filed on Apr. 3, 1998 by John E. McFee et al for a Multisensor Vehiclexe2x80x94Mounted Mine Detector. Amongst these methods, passive IR imaging is particularly attractive due to the simplicity of the technique, remote-sensing capability and relatively lower cost as compared to the other methods. This method has its own problems. In this technique, the mine signature is strongly dependent on the diurnal variations in solar illumination, type of soil, soil moisture content, and temperature gradient in the soil. A mine signature may be almost non-existent under cloudy conditions. Active infrared methods have been proposed for mine detection. These methods typically require the use of a scanning laser system and reflections from the mines (on the ground surface) could provide information on the location of the mines. Recently, P. Li et al in xe2x80x9cInfrared imaging of buried objects by thermal step-function excitationsxe2x80x9d, Appl. Optics, 34, pages 5809-5816, 1995, obtained results which indicate the possibility of imaging surface and buried mines through the use of thermal step function excitation using infrared heating lamps. In these hybrid sensing systems, the detection and illumination wavelengths regions are not too different in wavelength and the illumination wavelengths provide a limited penetration of the incident radiation to the depth of the mines. Limited target signature, background clutter and false alarms under various experimental conditions are the principal problems in these methods.
It is an object of the present invention to provide a landmine detection apparatus that improves on existing hybrid sensing systems by obtaining clearer infrared target signatures resulting in reduced detrimental effects of background clutter and the creation of false alarms.
A landmine detector, according to one embodiment of the invention, comprises a vehicle on which a waveguide with an antenna is mounted and having a high-power microwave source coupled to the waveguide wherein the antenna is positioned above a ground surface over which the vehicle may travel at a distance such that an output from the antenna can irradiate the ground surface, an infrared camera being mounted on the vehicle and positioned to obtain thermal signatures of the ground surface where an output of the antenna is directed when that surface is irradiated with microwave energy from said antenna, the thermal signatures providing indications as to the possible presence of any landmines buried in that area over which the antenna was positioned.